[Streams] Introducing the new Streams plugin (#198713)

## Summary

This PR introduces the new experimental "Streams" plugin into the Kibana
project. The Streams project aims to simplify workflows around dealing
with messy logs in Elasticsearch. Our current offering is either
extremely opinionated with integrations or leaves the user alone with
the high flexibility of Elasticsearch concepts like index templates,
component templates and so on, which make it challenging to configure
everything correctly for good performance and controlling search speed
and cost.

### Scope of PR
- Provides an API for the user to "enable" the streams framework which
creates the "root" entity `logs` with all the backing Elasticsearch
assets
- Provides an API for the user to "fork" a stream
- Provides an API for the user to "read" a stream and all of it's
Elasticsearch assets.
- Provides an API for the user to upsert a stream (and implicitly child
streams that are mentioned)
- Part of this API is placing grok and disscect processing steps as well
as fields to the mapping
- Implements the Stream Naming Schema (SNS) which uses dots to express
the index patterns and stream IDs. Example: `logs.nginx.errors`
- The APIs will fully manage the `index_template`, `component_template`,
and `ingest_pipelines`.

### Out of scope
- Integration tests (coming in a follow-up)

### Reviewer Notes
- I haven't implemented tests beyond a unit test for converting the
filter conditions to Painless. I wanted to get a PR up so we can start
iterating on the interface and functionality before we invest in
testing.
- You might need to add `server.versioned.versionResolution: oldest` to
your `config/kibana.dev.yaml` to play with the requests below in the
Kibana "Dev console".

### Example API Calls

Enable the root stream (and set the mapping for the internal `.streams`
index)
```
POST kbn:/api/streams/_enable
```

Read the root entity "logs"
```
GET kbn:/api/streams/logs
```

Fork the "root" entity "logs" and create "logs.nginx" based on a
condition
```
POST kbn:/api/streams/logs/_fork
{
  "stream": {
    "id": "logs.nginx",
    "children": [],
    "processing": [],
    "fields": [],
  },
  "condition": {
    "field": "log.logger",
    "operator": "eq",
    "value": "nginx_proxy"
  }
}
```

Fork the entity "logs.nginx" and create "logs.nginx.errors" based on a
condition
```
POST kbn:/api/streams/logs.nginx/_fork
{
  "stream": {
    "id": "logs.nginx.error",
    "children": [],
   "processing": [],
   "fields": [],
  },
  "condition": {
    "or": [
      { "field": "log.level", "operator": "eq", "value": "error" },
      { "field": "log.level", "operator": "eq", "value": "ERROR" }
    ]
  }
}
```

Set some processing on a stream and map the generated field
```
PUT kbn:/api/streams/logs.nginx
{
    "children": [],
    "processing": [
       { "config": { "type": "grok", "patterns": ["^%{IP:ip} – –"], "field": "message" } }
    ],
    "fields": [
       { "name": "ip", "type": "ip" }
    ],
  }
}
```

Field definitions are checked for both descendants and ancestors for
incompatibilities to ensure they stay additive.

If children are defined in the `PUT /api/streams/<name>` API,
sub-streams are created implicitly. If a stream is `PUT`, it's added to
the parent as well with a condition that is never true (can be edited
subsequently).

`POST /api/streams/_resync` can be used to re-sync all streams from
their meta data in case the Elasticsearch objects got messed up by some
external change - not sure whether we want to keep that.


Follow-ups

* API integration tests 
* Check read permissions on data streams to determine whether a user is
allowed to read certain streams

---------

Co-authored-by: Joe Reuter <johannes.reuter@elastic.co>
Co-authored-by: kibanamachine <42973632+kibanamachine@users.noreply.github.com>

docs/developer/plugin-list.asciidoc

@@ -897,6 +897,10 @@ routes, etc.
 |The stack_connectors plugin provides connector types shipped with Kibana, built on top of the framework provided in the actions plugin.
 
 
+|{kib-repo}blob/{branch}/x-pack/plugins/streams/README.md[streams]
+|This plugin provides an interface to manage streams
+
+
 |{kib-repo}blob/{branch}/x-pack/plugins/observability_solution/synthetics/README.md[synthetics]
 |The purpose of this plugin is to provide users of Heartbeat more visibility of what's happening
 in their infrastructure.